For reasons of saving energy, of increasing productivity and of improving the quality, it is desired to charge reheat furnaces continuously with hot products coming directly from the continuous casting run. However, it may happen that the process is interrupted for various reasons--the continuous casting suspends its production or the latter is insufficient to feed the hot-rolling plant--and in this case, it is necessary either to provide cold products from a storage yard or periodically to supplement the production of hot products from the continuous casting run with the same cold products from the storage yard.
Feeding the hot-rolling mill with a batch of products not having the same temperature causes quality problems in the outgoing products from the furnace. Overheating phenomena in hot products or underheating problems in cold products occur, causing energy losses and/or abnormal formation of scale.
Plants exist which partly solve the abovementioned drawbacks.
Thus, a first solution is known which consists in using a plant allowing intermediate furnace charging with hot products. A furnace is charged with cold products as soon as the furnace is started up. A furnace is charged with hot products via a side door in the furnace, at a point where the cold products have been able to reach the temperature of the hot products with which the furnace was charged.
However, this solution has a major drawback which limits its application. This is because side charging requires the use of an actual insertion device which is not easy to manipulate and which therefore is generally used only for charging with small-sized products (billets and possibly small blooms).
Moreover, a second solution is known which consists in using a reheat furnace. In this case, a reheat furnace is charged with hot products. With regard to cold products, they are introduced into a preheat furnace which heats them to the temperature of the hot products, before being transferred and then loaded with the hot products.
Again, this solution has a major drawback. This is because in this application the cold products arrive at the preheat furnace via roller tables. A loading device takes them and deposits them in the furnace. The cold products are then preheated to the temperature of the hot products and then unloaded by means of an unloading device and deposited on roller tables.
The hot products and the preheated cold products are then transported to the reheat furnace and are then seized by means of another loading device and taken into the reheat furnace in which they are heated to the hot-rolling temperature.
The use of a preheat plant necessarily requires the use of a certain number of loading and unloading devices and of transfer devices (roller tables), which result not only in an offset arrangement of the two furnaces--the preheat furnace and the reheat furnace--and hence a significant amount of the floor space being taken up, but also greater cooling of the products between the two furnaces, which phenomenon runs counter to reducing energy consumption.